Conventionally, stereotactic radiotherapy of the head has been developed first, which is directed to the head maintained still, and stereotactic radiotherapy of the trunk portion has been developed next, which carries out radiotherapy for the whole body in a state of the trunk portion fixed, by regarding a tumor of a treatment part as not movable either. However, when radiotherapy is carried out for the whole body in a state of the trunk portion fixed, the patient will be subjected to bodily pain and mental anguish. Besides, even if the trunk portion is fixed, the tumor of the treatment part is not necessarily in a fixed position without actually moving.
So, stereotactic radiotherapy has been developed in recent years, which carries out radiotherapy by placing a marker on a body surface of the patient, tracking the marker placed on the body surface using respiratory synchronization of the patient, and irradiating the treatment part with radiation when it comes to a predetermined position by respiration (e.g. expiratory cycles). However, the movement of the marker placed on the body surface and the movement of the tumor in the body are not necessarily in agreement.
So, a moving object tracking system for radiotherapy has been developed in recent years, which tracks also a tumor of a treatment part by embedding a marker near the tumor in the body, and tracking the marker by X-ray fluoroscopy. This moving object tracking system for radiotherapy carries out radiotherapy by irradiating the treatment part with radiation when the marker comes to a predetermined position (see Patent Document 1, for example).
The conventional moving object tracking system for radiotherapy has imaging systems as X-ray fluoroscopy for tracking the moving object, and the imaging systems includes X-ray tubes for emitting X-rays, and X-ray detectors (for example, X-ray detectors of the image intensifier or flat panel type) for detecting the X-rays. With the conventional stationary type moving object tracking system for radiotherapy, the imaging systems are fixedly arranged on a ceiling and a floor. Of the imaging systems, the X-ray tubes are arranged on the floor and the X-ray detectors are arranged on the ceiling, for example. Since the direction and position of X-ray fluoroscopy are fixed in this stationary type, two or more sets (e.g. four sets) of imaging systems are needed in order to carry out X-ray fluoroscopy from various directions.
In order to reduce the number of sets of imaging systems, the imaging systems are placed and moved on circular movable seats. Or each of the X-ray tubes and the X-ray detectors is moved along an arcuate track (e.g. arcuate rail) (see Nonpatent Document 1, for example). In this way, instead of the stationary type, the imaging systems including the X-ray tubes and X-ray detectors may be moved, thereby to reduce the number of sets of imaging systems and realize X-ray fluoroscopy from various directions.
In order to avoid a complicated drive system for driving the imaging systems, the X-ray tubes have fixed directions of irradiation, and the X-ray detectors have detecting planes with fixed directions. Therefore, as in Nonpatent Document 1 noted above, wherever on the arcuate tracks as shown in a plane view of FIG. 8, the X-ray tubes T have fixed directions of irradiation toward a tumor center (which is considered “isocenter” of treatment), and the X-ray detectors D have detecting planes with fixed directions for detecting transmitted X-rays from the isocenter, such being an arrangement of each. Therefore, even if their directions are fixed, the X-ray tubes T and X-ray detectors D are moved along the arcuate tracks, respectively, to be able to carry out X-ray fluoroscopy from various directions on the arcuate tracks.